Gear-cutting machine



W. C. FARNUM.

GEAR CUTTING MACHINE.

APPLICATION F|LED1uLY22.1918.

1,364,056. Patented Dec. 28, 1920.

2 SHEETS-SHEET 2.

UNITED STATES PATENT OFFICE.

WILLIAM C. FARNU'M, 0F WINCHENDON, MASSACHUSETTS, ASSIGNOR TO WILLIAM M. WHITNEY, 0F WINCHENDON, MASSACHUSETTS.

GEAR-CUTTING MACHINE.

Specification of Letters Patent.

Patented Dec. 28, 1920.

Original application filed May 24, 1917, Serial No. 170,660. Divided and this application filed July 22, 1918. Serial No. 245,982.

To all whom @'15 may concern Be it known that I, WILLIAM C. FARNUM, a citizen of the United States, residing at Winchendon, county of Worcester, and State of Massachusetts, have invented an Improvement in Gear-Cutting Machines, of which the following description, in connection with the accompanying drawings, is a specification, like characters on the drawings representing like parts.

The invention hereinafter described relates to cutters, and more particularly to spiral or scroll cutters for forming teeth of gears and for other purposes, and means for .operating such cutters in the production oi gears.

The present application is a division from my copending application Serial No. 170,660, tiled May 241, 1917.

The usual spiral cutter for forming curved teeth ci gears is so constructed that it cuts the concave profile ofa tooth on an arc having a radius shorter than the radius of the arc oi the convex profile of the tooth. As a consequence, when two such gears intermesh, the convex proiile oi a tooth oi one of the gears will not accurately iit and conform to the contour oi the concave profile oit ra tooth of the other gear, and the full strength of the teeth is not utilized in the transmission of power.

One oi the objects of the present invention is to provide a spiral cutter and means .for operating the same whereby teeth are formed, each having concave and .convex profiles of the same curvature. The construct-ion of the curved teeth produced is such that the teeth of intermeshing 4gears may accurately engage throughout the entire extent of the arcs crossing their pitch circles and gears with powerful transmission, long life and quiet operation are assured.

The usual spiral cutter is so constructed that it makes vcuts simultaneously on the concave and convex proiiles of the teeth.

Another object of the invention is to `provide means for operating a spiral cutter which makes a cut along one profile and then along the .other profile. In other words, the concave and convex cuts are made progressively. However, both cuts may be vmade in one rotation of the cutter, so that the teeth of the desirable character described are formed without loss in time.

The character of the invention may be best understood by reference to the following description of one good form thereof shown in the accompanying drawings,

ywherein `forming curved teeth on a gear blank;

Figs. 6, 7, 8 and 9 are views showing the relative positions of the cutter and gear blank in the course of the generation of involute gears;

Fig. 10 is a plan of a machine for supporting and operating the cutter and blank 'for the production of teeth on the latter;

Fig. 11 is a vertical section taken on line 11-11 of Fig. 10;

Fig. 12 is a perspective view of a pair of intermeshing gears having curved teeth produced by the cutter described herein; and

Fig. 13 is a perspective view of portions of the table and bed showing aydevice for limiting movement oit' the former along the latter.

Referring to the drawings The cutter shown therein as embodying the invention comprises a disk head 1 (Figs. 1 and 2) having a hub 3 internally threaded to permit the same to be secured to a suitable driving spindle. On this head is mounted means for forming the concave and convex proiiles of curved teeth.

To cut the concave proiiles of the teeth, in the present instance of the invention, a

cutter 5 is provided on said head comprisv ing a series of teeth, each having a forward cutting edge 9 vand a body 11 tapered rearward to furnish clearance. A leading tooth 13 and a final tooth 15 mark the limits of the series'of teeth of the cutter 5 which ilnay extend along an arc of substantially The outer edges of the teeth are adapted to cut the concave profile of the tooth in a blank, and are on radii progressively increasing in length'from the leading to the final tooth of the series. The radius r ot the final tooth determines the radius of the concave profile of the tooth.

To cut the convex profiles of the teeth, in the present instance of the invention, a cutter 17 is provided on said head comprising a series of teeth having forward cutting edges and tapered bodies similar to the teeth of the cutter for forming the concave profiles of a tooth. The final tooth 15 of the cutter for making the concave profiles of the teeth may constitute the leading tooth ot' the cutter for making the convex profiles ot the teeth. The final tooth 19 marks the other limit of the cutter, which also may extend along an are of substantially 180. The inner edges of these teeth cut the convex profiles of the teeth and are on radii progressively increasing in length from the leading to the final tooth of the series, but the radius fr ofthe final tooth 19 of the convex proiile cutter equals the radius r of the final tooth 15 of the concave profile cutter. Since the teeth` 15 and 19 make the inal cuts in producing the concave and convex profiles respectively of a tooth, and are of equal radii, it follows that the curvature of the arcs of said concave and convex profiles will be the same.

The concave profile forming cutter and the convex profile forming cutter, in the present instance of the invention, areV mounted on the same head, and are progressively disposed, so that they .make cuts successively along the concave andV convex profiles, but complete cuts are made on both profiles once in each rotation of the head.

It will be noted that the outer edges of the teeth of the concave cutter 5 form the Vconcave profiles of the teeth, whereas, the

inner' edges of the convex cutter 17 form the convex profiles ot the teeth. The inner edges ot the teeth of the concave cutter 5 are radially outward from the inner edges of the teeth of the convex cutter 17, and the outer edges of the teeth of the convex cutter are radially inward -from the outer edges of the teeth of the concave cutter;

`in other words, the profile-formingy edge of the Yconcave cutter 5 is upon the outer convex surface of this cutter, as indicated by the heavy arc in Figs. 3, 4t and 5, while the Y profile-forming edge of the convex cutter 17 is upon the concave surface of this cutter, as indicated by the heavy arc in these figures. As a result, the outer edges of the teeth of the concave cutter and Vthe inner edgesof the teeth of the convex cutter, are the vonly edges which are active in forming the concave and convex profiles of the teeth.

The concave and convex cutter, in the present instance of the Invention, are arprovided the radii of the final teeth of the two cutters are equal to produce final cuts on the concave and convex profiles of the teeth with the same curvature.

` Suitable means may be provided for supporting and rotating the cutter. present instance of the invention it is mounted on a spindle 21 (Fig. 10) journaled in bearings in uprights 23 on a stand-v ard 25, said spindle being adapted to Vbe driven at different speeds by stepped belt pulleys 27 i The cutter may be used to produce teeth in different articles. In the present exempliiieation of the invention, it is shown as used for cutting curved teeth in spur gears.

The gear blank 29 (Figs. V10 and 11) is In the supported in a horizontal plane transversely Y to the plane of the cutter.

VTo accomplish this,

a table 31 is mounted on a bed 33 supported on the standard and provided with a do'vetailed projection 35 adapted to slideY in a similarly shaped guideway in said Vbed to allow the table to be moved ,in a direction parallel to theaxis of the spindle; To feed the table, the usual screw 37 having a-hand wheel 38 may be threaded in said table and confined against axial'movement relative toV said be'd. Inward movement of the table toward the cutter may be limited by a screw 39 (Figs. 10y and 13) threadedl in an ear 4.1.1 projecting from said bed and adapted to engage a lug Z13 projecting from said table in linewith said screw.

To position thev blank on the table. they latter is provided with uprights (Fig. 11) having a bridge-bar 17 hinged' to Vone and adapted to be locked to the other bya swing bolt 19.

A mandrel 51 is vertically disposed between said uprightsy and has conicalV ends adapted to seat in conical bearings in an upper plug 53 threaded insaid' bridge-lan'.

and in a lower plug 55'mounted on sai-1l 'Y table. YThe upper plug'may be adjusted to.

take up wear and secure the mandrel 'accu rately iny position'without lost motion.

The gear blank may be mounted on av sleeve 57 on said mandrel, said sleeve having a vtoot 59 adapted torest against the upper end of a boss'` bearing 61 projecting` somewhat above said table. Thev gear blank may be Vsupported the appropriate distance above the'table to be acted upon bylthe cutter by a spacing washer 6B interposed between the foot of the sleeve and the lower face'of the blank.`

As the spiral cutter is rotated, it is essenA tial that the gear blank should be rotated. When a spiral cutter such as shown herein is employed, it is necessary to rotate the blank a distance equal to the pitch of the teeth to be formed on the blank in the course of each rotation of the cutter, and since the cutter is rotated continuously, the blank should be rotated continuously.

To rotate the blank as described, a master gear 65 (Figs. 10 and 11) may be mounted on the sleeve sustaining the blank, amd may be spaced from the blank by a washer 67. To secure the blank and master gear to the sleeve, a nut 69 may be threaded on said sleeve adjacent the top thereof, and engage the upper end of a washer 71 interposed between said nut and master gear. Then the nut is adjusted toward the foot of the sleeve, it will confine the blank, the master gear, and the spacing washers between them. Consequently, rotation of the master gear will be shared by the blank.

Suitable means may be provided for driving the master gear. In the present instance of the invention, this may be accomplished by a spiral gear 73 (Figs. 10 and 11) fast on one end of a shaft 75 journaled in a bearing 7 7 mounted on the table referred to. An elongated gear 79 fast on the opposite end of said shaft meshes with a pinion 81 fast on a shaft 83 journaled in bearings in the ups rights 23 referred t0. The shaft 83 may be driven by a gear 85 fast thereon meshing with an idler gear 87 mounted onv a stud shaft carried by one of the uprights 23, said idler gear being driven by a pinion 89 on the cutter spindle 21.

By the gear train described, the master gear may be conveniently driven from the cutter spindle. I/Vhen the table is fed toward the cutter, the elongated gear 7 9 may slide along the gear 81 without loss of engagement therewith, so that the automatic driving of the mastei gear may continue without interruption while the table is fed toward the cutter.

In operation, the bridge-bar 17 is swung to its position shown in dotted lines in Fig. 11, and the sleeve with the geai blank and master gear secured thereto is slid down onto the mandrel, and the bridge-bar is secured in its position shown in full lines in Fig. 11. rIhen the spindle is rotated, thereby rotating the cutter and the blank.

Comprehension of the operation of the cutter may be facilitated by reference to the cycle of its operations illustrated in Figs. 3, 4, and 5. In Fig. 3 the concave cutter 5 is shown with its leading tooth 13 starting to cut the concave roiile of a tooth along the arc a-a. In iig. 4t the cutter has rotated through an arc of 180.0, thereby causing the series of teeth of the concave cutter 5 to perform their cuts, and bringing the final tooth 15 to the position formerly occupied by the leading tooth 13. The final tooth is now completing the cut along the concave profile of the tooth and on the radius r referred to.

The inner edge of the final tooth 15 constitutes a part of the convex cutter 17, and is shown commencing the convex cut along lines 7;-22 in Fig. 4. Vhen the cutter rotates through a further arc of 1800, the leading tooth and the final tooth of the con- Vex cutter are carried around to their positions shown in Fig. 5, where the final tooth is shown completing the cut along the conveX profile of the tooth on line b-Z).

This marks the completion of concave and convex profile cuts, and brings the concave cutter 5 back to the position which it had at the commencement of the cycle. It will be noted that as the final tooth of the convex cutter is completing its out, the leading tooth of the concave cutter is commencing a new concave cut along the line c-c.

The final tooth of the convex cutter conipletes its cut on the radius r, which, as stated, is equal to the radius 1, and consequently, the arcs of the concave and conveX profiles of the tooth have the same curvature.

The cycle of operations performed Vby the cutter during one rotation thereof, has` just been described. The blank is rotated an increment equal to the pitch of the teeth to be cut on the gear blank by rotation of the blank through the master gear and the train of gears described, it being understood, that said train is appropriately designed to transmit the proper increment of rotation to the gear blank during one rotation of the cutter.

The cutter and the gear blank will continue t0 rotate until teeth have been partially formed throughout the circumference of the blank. Then the table may be fed inward toward the cutter, in order to produce deeper cuts in the blank. The table may be fedon and in toward the cutter until the teeth in the blank of the required depth are completed. rIlhe screw 39 may be adjusted to engage the stop lug i3 on the table at the proper` time to automatically insure cutting teeth of the requisite depth.

The rotation of the gear blank an increment equal to the pitch of the teeth to be formed on the blank serves to bring the blank progressively in relation to the cutter to generate involute teeth.

This operation is illustrated in the diagram shown in Figs. 6, 7, S, and 9. In Fig. G the cutter is shown commencing to enter the blank. In Fig. 7 the blank is shown in its position after it is rotated a distance equal to the pitch of the teeth, thereby partially producing the curved profiles. In Fig. 8 the blank is shown fed sufliciently in toward the cutter to produce the teeth of the required depth. In F ig. 9 the blank is shown in its position after being rotated the distance equal to the pitch of the teeth, thereby completing the involute proile of the tooth space.

After the teeth have been cut throughout the circumference of the blank, the machine is arrested, the bridge-bar is released, and the master gear, and the gear thus 'formed are removed from their supporting sleeve.

It will be apparent that by the cutter described, curved teeth may be quickly and perfectly formed, each having convex and concave profiles cut on arcs of the same curvature. The uniform identical construction of the teeth as described, enables a pair of such gears, for example, the gears 91 and 93 (F ig. 12) to accurately mesh with the convex proiiles of the teeth of one of the gears engaging throughout the lengths et the concave profiles of the other gear. As a result, the full power of the teeth is utilized, the lite of the gears is prolonged, and quiet operation is assured.

The active profile forming edges of the teeth of the concave and convex forming cutters, in the present instance of the invention, are substantially true spirals, While the opposite edges of said cutters are offset cutivardly and inwardly from continuations of said spirals indicated by broken lines in Fig. l.

The cutter may not only be used to produce curved teeth of gears such as described, but also may be used to produce curved 'teeth on beveled gears andrteeth on devices for other purposes as desired.

It will be understood that the invention is not limited to the speciiic embodiment shown, but that various deviations may be made therefrom, Without departing from the spirit and scope of the appended claims.

Claims:

l. In a machine of the character described, the combination of a cutter coin-r prising amember having spiral toothed cutters thereon, one for forming a concave profile of a tooth in a blank, and the other for forming a convex prolile of the tooth With the samecurvature as said concave profile, and means to rotate said cutter.

2. In combination, a cutter comprising a member having spiral cutters thereon, one for cutting the concave prole of a tooth in a blank, and the other for cutting the convex profile of said tooth, said cutters having portions of equal radii for producing concave and convex'proles of the same vcurvature, and means to rotate said member, and means to support and rotate said blank on its ams.

3. In combination, a cutter comprising a memberI having spiral cutters thereon, one for cutting the concave profile of a tooth in a blank, and the other for cutting the convex profile of said tooth, said cutters having portions of equal Vradii for producing concave and convex profiles of the same curvature, means to continuously rotate said member, and means to continuously rotate .said blank.

t. In combination, a cutter comprising a member having spiral cutters thereon, one for cutting the concave profile of a tooth in a blank, and the otherfor cuttingthe conxave and convex profiles of the sameY curva-,f

ture, means Vto rotate said blank, means toA rotate said member about an axis extending at rightY angles to the axis of said blank, to thereby produce curved Ateeth having the chord uniting the extremities of the concave and convex profiles lying parallel tothe axis of said blank.

In testimony whereof I have signed my name to this specification.

WILLIAM C. FARNUM. 

